Nuclear physics Flashcards
History of nuclear physics
- Democritus - came up with word ‘atomos’ (atoms)
- Joseph Priestley and Antoine Lavoisier; Age of Enlightenment.
- John Dalton; father of modern atomic theory
- JJ Thompson: Plum Pudding diagram
- Ernest Rutherford - Rutherford’s Scattering experiment; firing alpha particles at a very thin gold foil (one atom thick) in a vacuum. Scintillator (machine which lights up when atoms hits it) is placed behind.
About 1/8000 particles deviated away from in line with gold foil. 1/15-20000 not detected.
This is because some bounced back - something very small and dense must be at the center of the atoms. It must be very positive to bounce back from a positive alpha. This was the discovery of the nucleus. Particles which deviated away from the gold foil had a slight deflection as they were slightly repelled by the +ve nucleus.
Conclusions:
Nucleus is tiny, positive and most of mass of atom is concentrated.
Most of atom is empty space.
The closer things are to one another…
…the greater the force of repulsion
When is all kinetic energy transferred to electric potential energy
Graph for when electrons are attractive/ repulsive
Draw the diagram and graph showing electron diffraction
Half life def
The time taken for the number of unstable nuclei to fall to half its original value
What type of nuclear substance is good for inserting into the body and why
Technetium 99:
- suitable half life of 6 hours, so technetium will have lost radioactivity in a small enough amount of time.
- non-toxic
- gamma emitter
- suitable energy of gamma rays: not too energetic ( would cause damage), but energetic enough to measure on a gamma camera
What factors must be considered when choosing a nuclear substance to inject into someone
- non-toxic
- gamma emitter
- suitable energy of gamma rays
- suitable for job you wants (e.g will it go to e.g kidneys)
Draw an energy level diagram for molybdenum to technetium to rubidium
Half life def
The time taken for the number of unstable nuclei to fall to half its original value
What is one atomic mass unit (1u) equal to
1/12 of the mass of a neutral carbon atom
What is the mass defect/ binding energy
the difference between the mass of a nucleon in theory and the actual mass measured
- equal to The energy released when the nucleus forms
- equal to the energy required to separate the nucleons in the nucleus (typically in MeV)
What is the highest binding energy per nucleon (from the binding energy curve) possible and for what element is this from
8.8 MeV - from Iron 56
What is the most stable element and why
Iron 56 - this element requires the largest amount of energy to separate the nucleons in the nucleus (highest binding energy per nucleon)
Draw and label a diagram of the binding energy table
what is the difference between stable and unstable nuclei
- The most stable nuclei have roughly the same number of protons as neutrons
- If there were too many protons, then the repulsive force created by them all having the same positive charge, would cause the nucleus to repel when it becomes very large
- Therefore, if a nucleus has an imbalance of protons or neutrons, it is more likely to decay into small nuclei until it gets to a stable nucleus with roughly the same number of each
what does it mean and what is the issue with a nucleus being too heavy
- If an nucleus is too heavy, this means it has too many protons and neutrons
- The forces in the nucleus will be weaker in keeping the protons and neutrons together
- This can also cause the nucleus to decay
what happens to the mass number and atomic number in alpha decay
The mass number decreases by 4
The atomic number decreases by 2
Describe alpha or beta decay and draw a diagram of alpha decay
what happens to the mass number and atomic number in beta decay
- mass number of the decaying nuclei remains the same
- Electrons have an atomic number of -1
This means that the new nuclei will increase its atomic number by 1 in order to maintain the overall atomic number before and after the decay
what happens to the mass number and atomic number in gamma decay
Gamma decay does not affect the mass number or the atomic number of the radioactive nucleus, but it does reduce the energy of the nucleus
mass defect def
The difference between an atom’s mass and the sum of the masses of its protons and neutrons
what does the mass defect imply about the difference in mass between separated nucleons and a system of bound nucleons
A system of separated nucleons has a greater mass than a system of bound nucleons
binding energy def
The amount of energy required to separate a nucleus into its constituent protons and neutrons